In recent years, pocket paging devices, or beepers, that produce a vibration instead of an audible signal to alert a user have increased in popularity. As a result of this increase in popularity, improvements in the motor devices used to generate such a vibration alert signal have been demanded and made.
An example of one such motor device, which employs a hollow cylindrical coreless motor, is illustrated in FIG. 15. This device has a rotor consisting of a cylindrical coil 1, a support 2 for the cylindrical coil 1, a commutator 3 formed on the support 2, and a rotary shaft 14 rotatably supported through the center of the support 2. The rotary shaft 14 of the rotor is inserted through a hollow cylindrical field magnet 5 and is supported by a bearing 7 positioned at one end of a cylindrical housing 6 and a bearing 8 positioned at the other end of the housing 6. Usually, in the case of a coreless motor device of this configuration, an eccentric weight 10 with an offset center of gravity is installed at the tip of the rotary shaft 14 and a brush 9 is provided to contact the commutator 3.
Where the motor device is to be used in a portable environment, it is desirable to make the motor as small as possible. As can be seen in FIG. 15, construction of such a cylindrical coreless motor device, however, requires hollow drilling of the field magnet 5 in order that the rotary shaft 14 can be inserted through the field magnet 5. The required hollow drilling into a small diameter magnet, such as field magnet 5, however, is very difficult and consequently miniaturization of the motor device is limited.
In order to solve the shortcomings of such conventional motor devices and to develop a smaller motor device without the difficulty of performing hollow drilling of a small diameter magnet, a motor device as shown in FIG. 16, for example, was developed. The motor device illustrated in FIG. 16 has a rotor including a cylindrical coil 1 for a cylindrical coreless motor, a support 2 for the cylindrical coil 1, a commutator 3 formed on the support 2, and a rotary shaft 14 rotatably supported through the center of the support 2. The rotary shaft 14 is supported by a bearing 11 formed at one end of the cylindrical field magnet 15, which is affixed at an opposite end to one end of a cylindrical housing 6, and a bearing 13 mounted in a brush housing 12 positioned at the other end of the cylindrical housing 6. The rotary shaft 14 extends out from the housing 6 on the opposite side of the magnet 15 and functions as an output shaft.
A brush 9 is installed in a brush housing 12, and a lead wire 16 is connected. A cone-shaped central hole 17 is made at the center of the magnet 15 on the side nearest bearing 11 and the rotary shaft 14 is supported by a ball 18 that bears the thrust load of the rotary shaft 14. Alternatively, instead of using the above ball 18, a configuration such as shown in FIG. 17 could be used where a hard plate 19 is placed on the surface of magnet 15 and the rounded end of a rotary shaft 14 is supported in direct contact with the hard plate 19.
Since these coreless motor devices are constructed such that the rotary shaft 14 does not pass through the magnet 15 and the output shaft is placed at the opposite side of the magnet 15, the diameter of the magnet 15 can be smaller. Consequently, miniaturization of the motor is more easily accomplished. When the support for brush 9 and the bearing housing are to be made integral, the parts can be made compact and miniaturization and manufacturing of the motor is simplified. In addition, by installing the bearing 11 at the tip of the magnet 15 to bear the thrust load, torque loss caused by friction is reduced. It is a noteworthy fact that this novel configuration made miniaturization of cylindrical coreless motor devices possible.
Furthermore, it should be noted that the coreless motor device of this configuration includes an eccentric weight 10 with an offset center of gravity that is installed at the tip of the rotary shaft 14. Typically, as shown in more detail in FIG. 18, this weight 10 is fabricated from a metal of high density such as tungsten to form a semicircular part 70, a hole 71, and a raised portion 72. Weight 10 is typically installed on the rotary shaft 14 of a small cylindrical coreless motor 73, which operates to rotate weight 10. However, in the case of such weights having the form as shown in FIG. 18, a problem results in that the weight does not generate sufficient rotational force, and thus vibration, when it is miniaturized and made lighter. In addition, as a consequence of miniaturization, a very thin shaft is used as rotary shaft 14, and thus rotary shaft 14 of motor 73 is easily bent during operation.